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A unique feature of Quantum Cascade lasers is the possibility to stack active regions. Using a three stack heterogeneous Quantum Cascade laser ultra broadband amplification and short pulse generation is demonstrated. High power output is achieved by two stacked symmetric active regions.
In this contribution we study the fundamental interactions of a metamaterial system built of dipole elements in the THz regime. We investigate the coupling between the elements for different geometries, as well as symmetric and asymmetric structures and analyze the response of the system with changing refractive index of the surrounding medium. Finally, we use these structures to access intersubband...
By introducing side-absorbers to metal-metal waveguides of broadband terahertz quantum cascade lasers, we are able to control and completely suppress higher-order lateral waveguide modes. This change leads to an octave spanning laser spectrum with a 600 GHz wide flat top. In addition, the absence of higher order lateral modes has a strong effect on the pulse generation of injection seeded QCLs. We...
Time-domain terahertz spectroscopy (THs-TDS) has demonstrated its power in last two decades. With technological development of ultra-fast lasers and THz photonics, the sensitivity, signal dynamic range and the speed of acquisition of spectral information have been continuously improved. Here we present a proof of the principle of a confluence of THz-TDS and quantum cascade laser that holds promise...
Availability of coherent and relatively powerful terahertz sources — quantum cascade lasers (QCL) [1, 2] — opens the terahertz frequency range to application. However massive usage of THz-QCLs is hindered by necessity to cool them bellow 200 K, or if decent THz output power is required even to level of 77K or less. The reason for limited operation temperature range of THz-QCL lays in low energy of...
The generation of few-cycle Terahertz radiation into the free space from a biased photoconductive gap illuminated by an ultrashort laser pulse is known more than a decade [1]. Since then, many attempts were presented to increase the generated THz power without compromising the bandwidth of the output radiation [2, 3]. In this contribution, we report on a low-temperaturegrown GaAs (LT GaAs) based photoconductive...
We demonstrate an amplification of broadband terahertz pulses in the bandwidth of 500 GHz centered at 2.5 THz. The amplification is based on gain switched quantum cascade structure width the heterogeneous active region.
Two clay minerals from the kaolin group, namely well-ordered kaolinite and poorly ordered halloysite, were investigated by terahertz time-domain spectroscopy (THz-TDS). Both clay samples were used for preparation of their respective intercalates using dimethyl sulfoxide (DMSO) and potassium acetate (KAc) with water. The intercalates were also characterized by X-ray powder diffraction and Fourier transform...
Quantum cascade lasers (QCLs) operating at terahertz frequencies (1–10 THz) become a powerful radiation source with potential applications in medicine, environmental monitoring, security applications and communication. The development of QCLs is strongly focused on the optimization of unipolar carrier transport with prospect of high temperature operation (i.e. above cryogenic temperatures). Therefore,...
Metallic wire grids (WG) are popular terahertz (THz) polarizing elements. For freestanding structures, the near perfect properties of metals provide high transmission efficiency and extinction ratio over a wide frequency range. For substrate-supported structures however, these nearly ideal properties are lost as the transmission efficiency is dictated by the refractive index of the substrate. Recently,...
In this contribution, effective coupling between intersubband optical transitions and planar metallic resonators is presented. We discuss and demonstrate features unique to such a system and point out the consequences for active terahertz metamaterial devices.
The interaction of metamaterials and terahertz intersubband transitions is investigated in the strong coupling regime. We demonstrate that the resonant frequency of the metamaterial can be tuned by etching without destroying the strong interaction.
We have developed a scanning laser terahertz imaging system with 1.56 μm femtosecond fiber laser for high-speed and high resolution measurement. Using this system, we succeeded in obtaining high-resolution THz images of various samples. An imaging speed of about 47 seconds/image for 512 × 512 pixels and a spatial resolution of up to 56 μm were achieved.
We investigated the spatiotemporal terahertz (THz) near-field distribution of a split ring resonators (SRR) matrix using a real-time THz microscope. The near-field THz imaging analysis on a large area revealed the photonic crystal properties of the SRR matrix. This technique may open a door for the development of high sensitivity biosensors.
Since the first demonstration of the electro-optic detection of coherent free space electromagnetic waves in 1996, this technique became a golden standard for the time-domain spectroscopy in the terahertz and mid-infrared frequency range. The detection principle is based on the Pockels effect leading to a terahertz (THz) electric field induced birefringence in the non-linear optical crystal. This...
There is an ever increasing interest in metamaterials due to the multitude of possible applications coming at relative low fabrication effort. One such application is the “lasing SPASER”, where the metamaterial connects freely propagating plane waves with an active medium, such as electrically or optically pumped semiconductor quantum wells (QW) [1, 2]. Thereby, a high quality factor (Q-factor) of...
Metamaterial active in the terahertz (THz) frequency region is very attractive due to its potential for building unique optical components, such as superlenses, using relative simple fabrication technique. The meta-atom, an elementary unit of the metamaterial, is an electromagnetic resonator with non-zero magnetic and/or electric dipole interacting with free space electromagnetic wave. All present...
The study of quantum cascade lasers (QCL) in the terahertz frequency region by the use of THz time-domain spectroscopy has gained a lot of interest within the last few years [1]. Good physical insight was obtained for THz QCLs employing a single plasmon waveguide (surface plasmon waveguide) [2,3]. In comparison to that the double plasmon or metal-metal waveguide QCL uses a metal/semiconductor/metal...
Visualization of the dynamics of the electromagnetic resonators used to build metamaterial is presented. Observed data provides detailed information on the interaction between free space radiation and the resonator.
We derive and discuss conditions for the heterodyning in electro-optic detector of the electric field. Proof of principle of this technique is provided for detecting terahertz radiation.
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